Currently a PiN diode having a pn junction and a Schottky barrier diode (SBD) having a carrier potential barrier generated by a difference of a work function between a semiconductor layer and metal are mainly used as the semiconductor rectifying device that rectifies an input current and outputs the rectified current. In the Schottky barrier diode, in order to relax an electric field applied to an interface between the semiconductor layer and the metal, there is a JBS (Junction Barrier Schottky barrier diode) in which an impurity region (for example, p type) having a conductive type different from that of a semiconductor layer (for example, n type) is disposed on a surface of the semiconductor layer. There is also an MPS (Merged PiN-diode Schottky-diode), in which an ohmic junction is established between the impurity region (for example, p type) and the metal of the JBS or contact between the impurity region and the metal is brought close to the ohmic junction, minority carrier injection is generated when a voltage exceeding a built-in potential (Vbi) between the impurity region and the semiconductor layer, and a resistance is decreased by conductivity modulation.
On the other hand, a wide bandgap semiconductor typified by silicon carbide (hereinafter also referred to as SiC) is expected to be a next-generation power semiconductor device. The wide bandgap semiconductor has a band gap wider than that of silicon (Si), breakdown field strength higher than that of Si, and thermal conductivity higher than that of Si. The low-loss power semiconductor device that can be operated at a high temperature can be implemented when the characteristics of the wide bandgap semiconductor are utilized.
In the MPS, forward characteristics are achieved at a low resistance when the voltage at which the conductivity modulation is generated is decreased, and a large amount of current can be discharged at the low forward voltage when a forward surge current flows in. When the current larger than that in a steady state flows in, the current causes crystal destruction due to heat generation, junction destruction in the electrode, and the like under the following equation, current×voltage=power. On the other hand, when the large current can flow at the low forward voltage, the heat generation is suppressed to decrease a destruction ratio of an element.